I recently wasted a few minutes of +Valerie Doeringsfeld's life teaching her how gasoline, valves, cylinders, pistons and spark plugs work together to turn the wheels on her SUV. And I can tell you with 100% confidence that she'll have absolutely no interest in learning about the rest!

But for those of you that are into this sort of thing, these animated gifs do a really good job of visually explaining this and the rest of the engine system concepts.